What is the different usage between "put off" and "postpone" ?
"Postpone" indicates that you have to delay a particular activity or appointment, but will definitely reschedule it for a future date.
"Put off" indicates that you are delaying something that you don't want to do, and will keep delaying it as long as possible.
These definitions are not written in stone, and some people might say "put off" when they mean "postpone", as in "Can we put off lunch until next week? This week is crazy and I don't have a spare moment."